1. Field of the Invention
The present invention relates generally to the field of semiconductor memory technology. More specifically, the present invention relates to a highly-scalable, single-poly non-volatile memory (NVM) cell having reduced memory cell size (<1 μm2) without degradation of memory characteristics.
2. Description of the Prior Art
Semiconductor memory devices have become more popular for use in various electronic devices. For example, non-volatile memory (NVM) is widely used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, and other devices.
Generally, NVM may be divided into multi-time programmable (MTP) memory and one-time programmable (OTP) memory. MTP memory is multi-readable and multi-writable. For example, EEPROM and flash memory are designedly equipped with some corresponding electric circuits to support different operations such as programming, erasing and reading. OTP functions perfectly with electric circuits with mere programming and reading functions. Electric circuits for erasing operation are not required in OTP.
Single-poly NVM designs have been proposed which reduce the additional processing cost. A single-poly NVM forms the charge-storage floating gate with a single layer of polysilicon. Because the single-poly NVM is compatible with regular CMOS process, it is applied in the field of embedded memory, embedded nonvolatile memory in the mixed-mode circuits and micro-controllers (such as System on Chip, SOC), for example.
There is a trend to make smaller and smaller NVM devices. As the NVM devices become smaller, it is anticipated that the cost per bit of a memory system will be reduced. However, the scalability of the prior art NVM cell is limited by the rule of implanting I/O ion wells that are implanted into the substrate to a junction depth that is deeper than the depth of the shallow trench isolation (STI) in the memory array region.